Cutinases and suberinases are polyesterases, which are able to degrade or partially depolymerise plant polyester waxes, i.e. cutin and suberin. Significant amounts of cutin/suberin are present in different agricultural and forest raw materials and by-products, such as birch bark and cork, berries, cereals, vegetables and their processing by-products. The presence of these waxes in plant raw materials may impair the industrial processing of plant materials due to their hydrophobic character and recalcitrant structure.
Modification of the polyesters would improve the processing and exploitation of several natural materials, and would reduce disposal of process co-products or wastes. These waste fractions could be exploited as a source of more valuable compounds, e.g. suberin-based oligoesters could be potential raw materials in lubricants and binders. The use of polyesterases improve the processing and exploitation of several plant materials, such as cereals, fruits, vegetables and berries, and also improve release and recovery of valuable bioactive and functional components from these raw materials.
Sustainable use of natural resources and waste management contribute to minimise waste production. The use of enzymes in synergy with chemical and physical processes is an environmentally friendly means to add value to waste co-products. Cutinases/suberinases can also be utilised e.g. in laundry and dishwashing applications to remove fats as well as in cotton bio-scouring and surface modification of man-made polyester fibres.
Although lipids and waxes are abundant constituents of different industrial products and lignocellulosic residues, only a limited set of lipid modifying enzymes, other than conventional lipases, are commercially available. Cutinases and suberinases are regarded as potential enzymes for modification of natural lipids and waxes, which cannot be hydrolyzed by conventional lipases.
A cutinase from the plant/human pathogen fungus Fusarium solani sp. pisi is the most studied cutinase so far (Carvalho et al., 1999), but cutinases have also been found in microorganisms such as Alternaria brassicicola (Trail and Köller, 1993), Botrytis cinerea (Gindro and Pezet 1999), Venturia inaequalis (Köller and Parker, 1989), Aspergillus oryzae (Maeda et al., 2005) and in certain Streptomyces species (Fett et al., 1992). All of the biochemically well-characterized cutinases are serine esterases, containing the classical Ser-His-Asp triad common in serine proteases and in several lipases. The characterized cutinases possess a pH optimum from neutral to alkaline.
Cutinases have been suggested for a number of uses of which only a few are mentioned herein. WO2004/029193 for example suggests the use of lipases including cutinases in fermentation processes, in particular in ethanol production processes. U.S. Pat. No. 6,255,451 relates to degradation of biodegradable polymers with lipase and cutinase. A great number of potential lipolytic enzyme production organisms have been listed, including i.a. Coprinus cinerius and Trichoderma reesei. However, there is no disclosure of lipases from these organisms. Garcia-Lepe et al., 1997 screened for lipase activity in autolysed cultures of fifty-one fungi from different genera and strains. Fungi from the genus Fusarium were found to be the best producers of lipase activity and they also showed a low activity on cutin and suberin. Aspergillus was also found to have some activity, whereas Penicillium species had very low activity. Other species and strains from genus Trichoderma, order Mucorales and class Basidiomycetes did not show lipase activity.
Cutinases are frequently produced by phytopathogenic fungi, because they are involved in the disruption of structural cutin polymer of higher plants. Cutinases are secreted proteins, which allow pathogenic fungi to penetrate through the cuticular barrier into the host plant during the initial stage of fungal infection. However, phytopathogenic fungi are undesirable sources of industrial enzymes due to negative user perceptions. In fact, food grade poly-esterases and suberin-processing enzymes are currently not commercially available. Thus there is still a need for novel and more efficient polyesterases. The present invention meets this need.